It is important to purchase good quality bass guitar leads and cables as with top end hi-fi systems the choice and quality of the cable can affect the sound quality and volume of the bass guitar. The lead should also be generally long enough to allow comfortable access between the amp and perhaps a vocal microphone or floor-mounted pedal board.
It is generally easy to identify low quality cable as it tends to have "microphonic" qualities much like a cheap guitar or bass pick-up. In other words the sound bleeds back from the cable resulting in loss of tone and volume. Some of the newer types of guitar/bass leads have built-in circuit breakers to enable the sound to be muted when the jack is being inserted or removed to prevent "pops" and "squeals" at high volumes.
The pick-ups on a guitar or bass are the device that amplifies the resonance and pitch of the strings using a series of magnets to create a magnetic field. A number of companies exist that can supply replacement pick-ups for particular models of bass or guitar and the replacement pick-ups are designed to match the exact size, dimension and impedance of the originals for ease of installation.
The better known brands of replacement pick-ups are from companies such as Seymour Duncan, Dimarzio, EMG, Bartolini and Kent Smith. Some of these suppliers have website tools that will help you to choose the right pick up by allowing the user to define certain sound criteria. The choices made relate to the desired sound and then the criteria are matched with certain characteristics of specific models of pick-up. Many pick-up manufacturers also have MP3 sound bites of how the pick-ups sound when in use which is a great aid for the purchaser.